A firefighter protective garment is usually a coat or a pant consisting of three or more functional layers of fire-resistant materials. The various layers are normally but not limited to the following:                the outer shell which provides protection against puncture, cuts, abrasion, and heat;        the moisture barrier—consisting usually of a woven or non-woven substrate to which a fire resistant semi-permeable polymer is coated or laminated—which provides resistance to penetration by liquids and blood-borne pathogens while permitting the transmission of perspiration away from the body of the firefighter.        the thermal barrier—usually consisting of one or more insulating layers of non-woven fabric quilted or laminated to a woven face cloth—which provides the bulk of the resistance to the transmission of heat from the external environment to the body of the firefighter.        
A common configuration and orientation of these layers in a firefighter garment is as follows: The outermost layer is the outer shell fabric. Moving inwards, the next functional layer is the moisture barrier. The last functional layer is the thermal barrier, usually orientated with the thicker and softer insulating layer facing the moisture barrier film and the face cloth towards the body of the firefighter.
The entire outer shell portion of the garment is normally constructed of the same type and weight of fabric throughout the garment, for example, it may be Nomex® IIIA weighing 7.5 ounces per square yard (oz/yd2). Additional layers of the same or different fabrics or materials may be added to various areas of the garment to increase the thermal insulation or abrasion resistance of those areas of the garment.
Similarly, the entire thermal barrier of the garment is normally constructed of the same weight and materials composition irrespective of its location on the garment, for example, a 3.25 oz/yd2 Nomex IIIA woven face cloth fabric quilted to a 4.0 oz/yd2 Nomex®/Kevlar® needle-punch felt. Additional layers of the same or similar thermal barrier material may be added to certain areas of the garment to provide additional thermal protection.
Similarly, the entire moisture barrier of the garment is normally constructed of the same weight and materials composition irrespective of its location on the garment, for example, a 3.3 oz/yd2 93% Meta-Aramid/5% Para-Aramid/2% Anti-Stat Facecloth Laminated to an ePTFE Film. Additional layers of the same or similar moisture barrier material may be added to certain areas of the garment to provide additional protection.
The firefighter garment, including its outer shell and thermal barrier, must pass the stringent performance requirements of NFPA 1971 if the garment is to be certified compliant with this standard and judged suitable for its intended use. Two critical tests in evaluating the protection and comfort of a firefighter protective garment are the Thermal Protective Performance (TPP) test and the Total Heat Loss (THL) test.
The TPP test assesses the ability of the three component layers of a firefighter garment to retard the transfer of radiant and convective heat from the external environment to body of the firefighter and the NFPA 1971 standard mandates a minimum performance standard of 35 (equal to a heat flux of 2 cal/cm2/sec×a minimum elapsed time of 17.5 seconds until the sensor records the equivalent of a 2nd degree burn).
The Total Heat Loss (THL) test simulates the transfer of metabolic heat through the three component layers of the firefighter garment from the body of the firefighter to his external environment via the mechanisms of conduction and evaporation.
THL performance is, for the most part, inversely proportional to TPP performance and the selection and construction of an outer shell and thermal barrier of a firefighter garment that increases one will usually decrease the other.
A human being involved in the activities of a firefighter generates metabolic heat that must be dissipated if he is to maintain healthy bodily function, and the principal means by which the clothed firefighter body dissipates metabolic heat is by perspiring. In the 1990s, a scientific study (called The Indianapolis Field Study) using human subjects was conducted under the auspices of the International Association of Fire Fighters (IAFF) and demonstrated conclusively and scientifically the physiological impact (ex. on core temperature, heart rate, weight loss, endurance, task performance, etc.) of differing levels of metabolic heat transfer of firefighter garments as measured by the THL test. As a result, the most recent edition of the NFPA 1971 standard mandates a minimum THL performance rating of 205 W/m2.
For a firefighter garment constructed using air-permeable outer shell and thermal barrier materials the THL is inversely proportional to the weight and thickness of those two layers. A firefighter garment with a lighter outer shell or a lighter thermal barrier will therefore have a higher THL than the same layers having a heavier weight.
U.S. Pat. No. 8,453,270B2 discloses a patterned heat management material to be used in garments, sleeping bags, footwear, etc. The object of this invention is to increase the comfort of the user of the object containing the material by retaining and equalizing the distribution metabolic heat through the mechanisms of reflection or conduction. It does not claim to facilitate the evacuation of metabolic heat, nor is it envisaged for use in a firefighter garment.
U.S. Pat. No. 5,469,581A discloses a sports garment for warmth with freedom of movement having thin sections and thick sections where inner arm areas and inner torso areas defined by the area of contact between the arms and torso of the wearer. This invention is designed to retain metabolic heat while aiding mobility. It does not facilitate the dissipation of metabolic heat via the strategic placement of thinner fabric elements.
U.S. Pat. No. 4,922,552 discloses firefighter's garments having maximally insulative, heavier liner materials in areas in which maximum thermal protection is required, such as shoulders, back, thighs, etc. It also has as an object to provide in the same garments lighter, more flexible liner materials 20 (hence, comparatively less thermal insulation) in areas which are flexed and/or which interface with other protective garments. It is not an object of this patent to increase the dissipation of metabolic heat; in fact, the incorporation of heavier liner materials will invariably increase the retention of metabolic heat.
U.S. Pat. Nos. 5,299,602 and 5,323,815A disclose, respectively, textile materials used in the construction of the outer shell and inner lining of a firefighter protective garment, which by being lightweight increase wearer comfort, reduce metabolic energy requirements and decrease metabolic heat build-up. It is an object of these two patents to permit the construction of a firefighter garment that is as light as possible while still respecting the thermal and mechanical performance requirements of NFPA 1971 but they do not have as an object the design or construction of such a protective garment. Furthermore, since there is no claim of using differing weights of the fabrics in different areas of the garment to maximize metabolic heat dissipation and since we know that THL and TPP performance are inversely proportional, a firefighter protective garment made with these materials would theoretically have good THL performance everywhere on the garment, even where it is not needed, and as result, only marginal TPP performance everywhere on the garment, even where higher TPP performance is desirable.
U.S. Pat. No. 3,710,395A discloses an air distribution garment consisting of a layer of an air-permeable, stretchable, compression-resistant, spacer fabric enclosed between layers of stretchable, air-permeable, fabric, having air inlet openings on said garment communicating with manifolds within the garment and through which air is caused to flow over the back and chest portions through the spacer fabric. The object of this invention is to remove excess heat and moisture from the torso to maintain the body in thermal balance. However, the description of the preferred embodiments reveals that the invention is intended to be worn underneath a regular or special-purpose garment and is not intended as a protective garment itself. If it were, the NFPA 1971 performance requirements mandating a level of impermeability to water and to blood-borne pathogens (and as a consequence to air) would render non-compliant with said standard, any firefighter garment incorporating said invention.
However, in light of the aforementioned, there is still a need for a firefighter garment which, by virtue of its design and components, would be able to provide better air circulation between the garment and the wearer thereof.